Condemned house: A condemned house cannot be refreshed, and will decay within 5 days. Houses will become condemned if a player places or acquires a newer house on any shard.

Condemned Houses

A condemned house is a house that will decay and fall down after 5 days. If a house is condemned, this fact will be noted on the house menu. (See the image on the right)

Why do houses go condemned?

If you own a house on any shard, placing or buying another house will condemn your existing one. You can only have one house per account. You can safely use the house placement tool to check spots and see if they'll fit a house, as long as you do not actually confirm that you want to place a house.
If your account goes inactive, your house(s) on it will be condemned after a 90-day grace period.
Note that if you get rid of all other houses except the condemned one, it will no longer become un-condemned again automatically after shard maintenance in the morning, like it used to before the release of Age of Shadows! The only way to un-condemn a house is to sell or give the house away to someone else, or demolishing and re-building it (but be careful of the 7-day waiting period!).